My Uncle Noach zt”l taught: The Mishna says we should hear with our ears. That seems obvious—we don’t hear with our eyes! But the truth is that most of us don’t hear with our ears. We hear with our brains and our emotions.
But saying the Shema, we have to more than hear—we have to listen. And that’s why we have to say the words,and not just read them. We have to listen to what we are saying. So that the words themselves will have their effect on us—so that we feel that Shema Yisrael is talking to us as individuals.